Fluid pressure generating means

ABSTRACT

A fluid pressure generating means ( 10 ) for a heart assist device having blood pumping means. The pressure generating means ( 10 ) includes a housing ( 11 ), defining an interior volume ( 18 ), and having a substantially rigid first housing portion ( 12 ), a substantially rigid second housing portion ( 14 ), a flexible third housing portion ( 16 ) extending between the first ( 12 ) and second ( 14 ) housing portions and an inlet/outlet port ( 15 ) adapted for fluid communication with the blood pumping means. The pressure generating means ( 10 ) also includes a fluid filling the housing and a motor ( 20 ) disposed within the housing ( 11 ) and connected between the first ( 12 ) and second ( 14 ) housing portions. Actuation of the motor ( 20 ) moves the first ( 12 ) and second ( 14 ) housing portions relative to one another to generate fluid pressure changes at the inlet/outlet port ( 15 ). A related heart assist device and method for the treatment of congestive heart failure, myocardial ischemia and like conditions are also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates to a fluid pressure generatingmeans for use with a heart assist device.

BACKGROUND OF THE INVENTION

[0002] The applicant's international PCT patent application no.PCT/AU00/00654 (International publication no. WO 00/76288) entitled“Heart Assist Devices, Systems and Methods” (“the PCT application”)discloses numerous embodiments of a novel heart assist device adaptedfor implantation into a patient. Broadly speaking, the disclosed heartassist devices include: an aortic compression means adapted, whenactuated, to compress an aorta of a patient; a fluid reservoir; and afluid pressure generating means adapted to pump fluid from the fluidreservoir to the aortic compression means so as to actuate the aorticcompression means in counterpulsation with the patient's heart. Therelevant portions of the PCT application are incorporated herein bycross-reference.

[0003] It is a first object of the present invention to provide improvedfluid pressure generating means suitable for use with the aorticcompression means described in the PCT application. It is a secondobject to provide a fluid pressure generating means which may be placedmore conveniently into the body of a patient.

SUMMARY OF THE INVENTION

[0004] Accordingly, in a first aspect, the present invention provides afluid pressure generating means for a heart assist device having bloodpumping means, the pressure generating means including:

[0005] a housing, defining an interior volume, and having asubstantially rigid first housing portion, a substantially rigid secondhousing portion, a flexible third housing portion extending between thefirst and second housing portions and an inlet/outlet port adapted forfluid communication with the blood pumping means;

[0006] a fluid filling the housing; and

[0007] a motor or other actuator means disposed within the housing andconnected between the first and second housing portions,

[0008] wherein actuation of the motor or other actuator means moves thefirst and second housing portions relative to one another to generatefluid pressure changes at the inlet/outlet port.

[0009] In one preferred form, the third housing portion has an outeredge about its periphery and inner edge about an opening and is joinedalong the outer and the inner edge to the first and second housingportions respectively.

[0010] In another preferred form, the third housing portion is connectedto only one of the first and second housing portions and abuts againstthe other of the first and second housing portions.

[0011] The blood pumping means is preferably adapted to displace bloodin the aorta, more specifically the ascending aorta, and preferably bycompressing or deforming the aorta of a patient in counter-pulsationwith the patient's heart. More preferably, the blood pumping means isadapted to displace blood from the ascending aorta of the patient. In analternative arrangement, the fluid pressure generating means can be usedto drive a conventional left ventricular assist device or anextra-ventricular co-pulsation heart compression device. In such anarrangement suitable valves are used to ensure the correct direction ofblood flow through a pumping chamber driven by the fluid pressuregenerating means.

[0012] In a further preferred form, one of the first and second housingportions is moveable and the other of the first and second housingportions is fixed, the moveable housing portion being exposed to theoutside of the heart assist device and adapted to interface with thelung of a patient.

[0013] In a yet further preferred form, one of the first and secondhousing portions is moveable and the other of the first and secondhousing portions is fixed, the moveable housing portion not beingexposed to the outside of the heart assist device and the deviceincluding a flexible compliance chamber. The compliance chamber isdesirably in contact with the lung of a patient.

[0014] The actuating means desirably includes a nut coupled to one ofthe first and second housing portions and a threaded shaft coupled tothe other of the first and second housing portions, the threaded shaftand the nut being threadedly engaged and the motor being adapted torotate the nut relative to the threaded shaft. In one arrangement, thenut is connected to the moveable one of the first and second housingportions and the threaded shaft is connected to the fixed one of thefirst and second housing portions. In another arrangement, the threadedshaft is connected to the moveable one of the first and second housingportions and the nut is connected to the fixed one of the first andsecond housing portions.

[0015] In an embodiment, the outflow of the fluid from the inlet/outletport is axial to the housing. In another embodiment, the outflow of thefluid from the inlet/outlet port is radial to the housing. In a furtherembodiment, the outflow of the fluid from the inlet/outlet port istangential to the housing.

[0016] A surface of the device is preferably curved to fit snugly withthe chest wall and/or mediastinum and/or diaphragm of a patient.

[0017] The blood pumping means is preferably in the form of a fluidoperated cuff adapted to surround the patient's aorta.

[0018] The fluid filling the housing is preferably a liquid. The liquidis preferably an oil or saline. The oil is preferably a silicone oil anddesirably has viscosity between 10 and 100 centistokes, most desirablybetween 10 and 30 centistokes.

[0019] In a second aspect, the present invention provides a heart assistdevice including:

[0020] a blood pumping means adapted, when actuated, to cause or assistthe movement of blood around the patient's vasculature;

[0021] a fluid reservoir;

[0022] a fluid pressure generating means adapted to pump fluid from thefluid reservoir to a housing containing both the fluid reservoir and thefluid pressure generating means that is so shaped and dimensioned as tobe adapted to lie in the plueral cavity, adjacent to the lung, when theblood pumping means is functionally positioned within the patient.

[0023] In a third aspect, the present invention provides a method forthe treatment of congestive heart failure, myocardial ischemia and likeconditions, the method comprising:

[0024] inserting into the plueral cavity within the chest (preferablythe right chest) of a patient, and adjacent to the lung, a housingcontaining a fluid reservoir and a fluid pressure generating meansadapted to pump fluid from the fluid reservoir to blood pumping meansfunctionally placed in the patient so as to cause or assist the movementof blood around the patient's vasculature.

[0025] Until now most implanted heart assist devices have been placed inthe abdominal cavity of a patient. This is disadvantageous as itcomplicates the surgical procedure and is unduly invasive for thepatient. The few proposals for placement of such a device in the chestcavity have proposed the placement of the device against the inside ofthe chest wall so that the device can be wired to the ribs of thepatient. It was apparently felt that this was necessary to support theweight of the device and to prevent it from moving around in thepatient. The present inventors have found that the device may be placedagainst the mediastinum directly adjacent the patient's heart andattached to surrounding soft tissue. The device will thus lie in theplueral cavity, adjacent to the lung. The device preferably lies in asagittal plane within the patient's body. Desirably, the device will nottouch the inside surface of the chest wall at all. This placement willreduce pain for the patient and make placement of the device easier forthe surgeon implanting the device.

[0026] Preferably, the blood pumping means referred to in the abovemethod is adapted to compress the aorta of a patient incounter-pulsation with the patient's heart. More preferably, the bloodpumping means is adapted to compress the ascending aorta of the patient.

[0027] In a fourth aspect, the present invention provides a heart assistdevice including:

[0028] a blood pumping means adapted, when actuated, to cause or assistthe movement of blood around the patient's vasculature;

[0029] a fluid reservoir; and

[0030] a fluid pressure generating means driven by an electric motor andadapted to pump a liquid from the fluid reservoir to the blood pumpingmeans;

[0031] the electric motor having a cogging torque which is sufficientlylow that the natural systolic blood pressure of the patient issufficient to cause liquid in the blood pumping means to be returned tothe fluid reservoir in the event that the electric motor stops.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Preferred embodiments of the invention will now be described, byway of examples only, with reference to the accompanying drawings inwhich:

[0033]FIG. 1 is a schematic longitudinal sectional view of a firstembodiment of a fluid pressure generating means according to theinvention;

[0034]FIG. 2 is a schematic longitudinal sectional view of a secondembodiment of a fluid pressure generating means according to theinvention;

[0035]FIG. 3 is a schematic longitudinal sectional view of a thirdembodiment of a fluid pressure generating means according to theinvention connected to a heart assist device;

[0036]FIG. 4a is a perspective view of a fourth embodiment of a fluidpressure generating means according to the invention;

[0037]FIG. 4b is an underside perspective view of a housing portion ofthe fluid pressure generating means shown in FIG. 4a;

[0038]FIG. 4c is a schematic longitudinal sectional view of the fluidpressure generating means shown in FIG. 4a; and

[0039]FIG. 5 is a schematic longitudinal sectional view of a fifthembodiment of a heart assist device according to the invention;

[0040]FIG. 6 is a perspective view of the device shown in FIG. 5; and

[0041]FIG. 7 is a perspective view of the device shown in FIG. 6 afterimplantation into the pleural cavity, medial to the lung, of a patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Referring firstly to FIG. 1, there is shown a schematiclongitudinal sectional view of a first embodiment of a fluid pressuregenerating means according to the invention, in the form of pump 10. Thepump 10 includes a housing, indicated generally by the reference numeral11, comprising a substantially rigid bell-shaped first housing portion12, a substantially rigid flat circular second housing portion 14 and aflexible third housing portion or membrane 16.

[0043] The first, second and third housing portions 12, 14 and 16together define an external boundary of the housing 11 around aninterior volume denoted 18, which is filled with a silicone oil. Thesecond housing portion 12 itself formed from a cone-shaped portion 12 awhich is sealingly connected, after assembly of the pump 10, to acylindrical portion 12 b.

[0044] The cone-shaped portion 12 a also includes an inlet/outlet port15, which is connected in fluid communication with an aortic compressionmeans or blood pumping means (not shown) by a conduit 17.

[0045] The membrane 16 is substantially annular in configuration and hasenlarged inner and outer edges 16 a and 16 b which are sealinglyreceived in corresponding circumferential recesses 12 c and 14 aprovided in the first and second housing portions 12 and 14respectively.

[0046] The pump 10 also includes an electric motor, indicated generallyby the reference numeral 20, within the interior volume 18 of thehousing 11. The motor includes a rotor 21, rotor laminations 22, magnets24, stator 25, stator laminations 26, end windings 28 and bearings 30.

[0047] The stator 25 is fixed to the housing portion 12 a by a number ofscrews 30 (only one shown). The rotor 21 is fixed to a nut 32, which isitself threadedly engaged with a threaded shaft 34 through ball bearings(not shown). The shaft 34 is fixed to the housing portion 14 by screw36. The stator 25 also includes a number of guide journals 38 (only oneshown) through which are guided a corresponding number of shafts 40 thatdepend from the housing portion 14.

[0048] Power and control signals are fed to the motor 20 through lines42 and 44 respectively.

[0049] The operation of the pump 10 will now be described. Energisingthe motor 20 to rotate in a first direction rotates the nut 32 relativeto the threaded shaft 34 which causes the threaded shaft 34 to move in adirection parallel to its longitudinal axis in a first directionindicated by arrow 46. FIG. 1 shows the shaft 34 at the end of itstravel in this direction and after driving the housing portion 14 awayfrom the housing portion 12 to increase the interior volume 18 and causea suction or negative pressure at the inlet/outlet port 15. This suctionactively deflates the aortic compression means (not shown).

[0050] Energising the motor to rotate in the opposite direction causesthe threaded shaft 34 to move parallel to the longitudinal axis in theopposite direction indicated by arrow 48 and draw the portion 14 towardsthe housing portion 12. The end limit of travel in this direction isindicated in phantom in FIG. 1 and, with reference to which it should benoted that, the guide shaft 40 abuts the inner surface of the housingportion 12 a at the limit of its travel at recess 50. Drawing theflexible portion 14 towards the housing portion 12 reduces the interiorvolume 18 which causes a positive pressure at the inlet/outlet port 15and drives fluid from the interior volume 18 to inflate the aorticcompression means.

[0051] The motor 20 is actuated cyclicly in this manner incounterpulsation with the patient's heart in response to signalsreceived from an ECG monitor or systemic arterial pressure, as disclosedin the PCT application.

[0052] Referring now to FIG. 2, there is shown a schematic longitudinalsectional view of a second embodiment of a fluid pressure generatingmeans according to the invention, in the form of pump 60. The pump 60 issimilar to the pump 10 shown in FIG. 1 and like features are indicatedwith like reference numerals. Differences between the pumps 10 and 60are described in detail below.

[0053] Firstly, the housing portion 12 a of the pump 60 includes anopening 62 sealed by a second flexible membrane 64 which forms acompliance chamber 65. The chamber 65 is in fluid communication with theinterior volume 18. Secondly, the inlet/outlet port 15 is provided in afurther housing portion 66 which is sealed with respect to the side ofthe second housing portions 14 and third housing portion 16 that isremote the motor 20. The housing portion 66 creates, in conjunction withthe housing portions 14 and 16, a second interior volume 68 in fluidcommunication with the aortic compression means or blood pumping means(not shown) via conduit 17.

[0054] The operation of the pump 60 is similar to that as described withreference to the pump 10 with the exception that the movement of thehousing portion 14 causes volume changes in the second interior volume68 which in turn inflates and deflates the aortic compression means. Themovement of the housing portion 14 also causes fluid movement in thepart of the interior volume 18 within the first, second and thirdhousing portions 12, 14 and 16 and these changes cause an identicalvolume change in the interior of the compliance chamber 65, which isshown having a decreased volume in response to the compression meansbeing inflated. The chamber 65 will have an increased volume in responseto the compression means being deflated, as is shown in phantom.

[0055] As the interior volumes 18 and 68 are maintained sealed from oneanother by the second and third housing portions 14 and 16, the pump 60can be configured to use different fluids in each of the interiorvolumes 18 and 60, as desired. For example, a saline solution can beused in the interior volume 68 and a lubricating oil can be used in theinterior volume 18 which contains the motor 20.

[0056]FIG. 3 is a schematic cross sectional side view of a thirdembodiment of a fluid pressure generating means according to theinvention, in the form of pump 80. The pump 80 is shown connected to anaortic compression means or blood pumping means in the form of cuff 82.The pump 80 is similar to the pump 60 described in relation to FIG. 2and like reference numerals will be used to indicate like features.Differences between the pumps 60 and 80 are described in detail below.

[0057] Firstly, the pump 80 has a first external substantially rigidcylindrical housing portion 84, a pair of second internal substantiallyrigid housing portions 86 a and 86 b and a third substantially flexiblehousing portion 88. The latter seals an end of the first housing portion84. The pump 80 also includes a second flexible housing portion 90 whichseals the other end of the second housing portion 84 and forms acompliance chamber 92. Secondly, the second housing portion 86 and thethird flexible housing portion 88 abut, but are not connected, to eachother.

[0058] The operation of the pump 80 is similar to that described withreference to pump 60 in that the motor 20 is energised to reciprocallydrive the threaded shaft 34 and thus the second housing portion 86 a indirections 46 and 48 parallel to the longitudinal axis of the threadedshaft 34.

[0059]FIG. 3 shows the pump 80 in a position after movement of thesecond housing portion 86 a in the direction 46 and driving fluid fromthe second interior volume 68 into the cuff 82 to inflate same. In thisposition, the second membrane of 64 is drawn into the interior of thesecond housing portion 84 to maintain the interior volume 18 constant.Driving the threaded shaft 34 in the opposite direction 48 results inthe housing portion 86 b forcing the membrane 64 to the position shownin phantom which is external the second housing portion 84. This alsoresults in the third housing portion 88 being drawn to the position alsoshown in phantom to maintain the interior volume 18 constant. Aspreviously described in relation to pump 60, when the third housingportion 86 is in this position fluid is drawn into the second interiorvolume 68 from the cuff 82 to deflate same.

[0060]FIGS. 4A to 4C show a fourth embodiment of a fluid pressuregenerating means according to the invention, in the form of pump 100.The pump 100 is similar to the pump 10 shown in FIG. 1 and likecomponents have been referred to with like reference numerals. However,the pump 100 has been designed to be as thin as possible (dimensions: 82mm long; 60 mm wide; and 45 nun deep) in order to allow positioning in apatient's chest in contact with the mediastinum adjacent the heart. Thepump 100 is placed with the planar housing portion 14 lying in asagittal plane and as with the edge of the housing 100 clear of theinside surface of the chest wall. This orientation is chosen so as tominimise pain and trauma to the patient and also minimise the length ofconduit required between the pump 100 and the aortic compression means(not shown). This positioning also assists the surgeon in placing thedevice.

[0061] Referring finally to FIGS. 5 to 7, there is shown a schematiclongitudinal sectional view of a fifth embodiment of a fluid pressuregenerating means according to the invention in the form of pump 120. Thepump 120 is shown connected to an aortic compression means or bloodpumping means in the form of cuff 122. The construction and operation ofthe pump 120 is similar to die pump 10 shown in FIG. 1 and like featuresare indicated with like reference numerals. The size of the pump 120 issimilar to the pump 100 shown in FIGS. 4A to 4C, except it is more ovateand has flattened sides (See FIG. 6). The ovate form of the pump 120 andthe positioning of the cuff 122 nearer one end allows the device to beplaced in the plural cavity, medial to the lung, and lying in a sagittalplane within the patient's body, as is shown in FIG. 7. The pump 120does not touch the inside surface of the patient's chest wall in thisposition. FIG. 7 also shows an external battery pack 123 which powersthe pump 120.

[0062] The main differences between the pumps 10 and 120 are as follows.Firstly, the flexible third housing portion 16 is sealingly connectedabout its outer edge 16 b to the substantially rigid ovate cup-shapedfirst housing portion 12. The connection and sealing is achieved by asealing rim 124 on the third portion 16 being snugly received in anannular recess 126 on the first portion 12. Secondly, the substantiallyrigid flat ovate second housing portion 14 is received within acorresponding recess in the third portion 16, on the interior side ofthe third portion 16, and is thus within the interior volume 18.

[0063]FIG. 5 shows the pump 120 in a position after movement of thesecond housing portion 14 in the direction 46, which draws fluid intothe interior volume 18 from the cuff 122 and deflates same. Driving thethreaded shaft 34 in the opposite direction 48 forces the second housingportion 14 towards the motor 20 (see the position of the shaft 34 shownin phantom). As previously described, when this occurs, fluid is forcedfrom the interior volume 18 into the cuff 82 to inflate same.

[0064] An advantage of the preferred embodiments of fluid pressuregenerating means described above is the liquid surrounding the motor isused both as a driving fluid to inflate/deflate the compressions (eitherdirectly as per the embodiments of FIGS. 1 and 4 exchanging fluid. Theliquid also dampens sound made by the pump mechanism. This simplifiesthe construction, and minimises the size, of the fluid pressuregenerating means.

[0065] Whilst the fluid pressure generating means will normally activelydrive both the inflation and deflation of the aortic compression means,the motor is preferably designed so that the cogging torque of the motoris sufficiently low that the natural systolic blood pressure of thepatient is sufficient to deflate the cuff. If the motor is inactivatedfor any reason with the cuff in an inflated condition (and thus with theaorta partially occluded), this arrangement means that the naturalsystolic blood pressure will deflate the cuff by pushing fluid from thecuff into the housing and passively driving the second housing portionaway from the motor.

[0066] It will be appreciated by person skilled in the art that numerousvariations and/or modifications can be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofinvention as broadly described. For example, the embodiments of theinvention are not restricted for use with the embodiments of the heartassist device shown in the PCT application. The specific embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. A fluid pressure generating means for a heart assist device havingblood pumping means, the pressure generating means including: a housing,defining an interior volume, and having a substantially rigid firsthousing portion, a substantially rigid second housing portion, aflexible third housing portion extending between the first and secondhousing portions and an inlet/outlet port adapted for fluidcommunication with the blood pumping means; a fluid filling the housing;and a motor or other actuator means disposed within the housing andconnected between the first and second housing portions, whereinactuation of the motor or other actuator means moves the first andsecond housing portions relative to one another to generate fluidpressure changes at the inlet/outlet port.
 2. The fluid pressuregenerating means as claimed in claim 1, wherein the third housingportion has an outer edge about its periphery and inner edge about anopening and is joined along the outer and the inner edge to the firstand second housing portions respectively.
 3. The fluid pressuregenerating means as claimed in claim 1, wherein the third housingportion is connected to only one of the first and second housingportions and abuts against the other of the first and second housingportions.
 4. The fluid pressure generating means as claimed in claim 1,2 or 3, wherein the blood pumping means is adapted to displace bloodfrom the aorta of a patient in counter-pulsation with the patient'sheart.
 5. The fluid pressure generating means as claimed in claim 4,wherein the blood pumping means is adapted to displace blood from theascending aorta of the patient.
 6. The fluid pressure generating meansas claimed in claim 1, 2 or 3, wherein the fluid pressure generatingmeans is adapted to drive a conventional left ventricular assist deviceor an extra-ventricular co-pulsation heart compression device.
 7. Thefluid pressure generating means as claimed in any one of claims 1 to 5,wherein one of the first and second housing portions is moveable and theother of the first and second housing portions is fixed, the moveablehousing portion being exposed to the outside of the heart assist deviceand adapted to interface with the lung of a patient.
 8. The fluidpressure generating means as claimed in any one of claims 1 to 5,wherein one of the first and second housing portions is moveable and theother of the first and second housing portions is fixed, the moveablehousing portion not being exposed to the outside of the heart assistdevice and the device including a flexible compliance chamber.
 9. Thefluid pressure generating means as claimed in claim 8, wherein thecompliance chamber is in contact with the lung of a patient.
 10. Thefluid pressure generating means as claimed in any one of the precedingclaims, wherein the actuating means includes a nut coupled to one of thefirst and second housing portions and a threaded shaft coupled to theother of the first and second housing portions, the threaded shaft andthe nut being threadedly engaged and the motor being adapted to rotatethe nut relative to the threaded shaft.
 11. The fluid pressuregenerating means as claimed in claim 10, wherein the nut is connected tothe moveable one of the first and second housing portions and thethreaded shaft is connected to the fixed one of the first and secondhousing portions.
 12. The fluid pressure generating means as claimed inclaim 10, wherein the threaded shaft is connected to the moveable one ofthe first and second housing portions and the nut is connected to thefixed one of the first and second housing portions.
 13. The fluidpressure generating means as claimed in any one of the preceding claims,wherein the outflow of the fluid from the inlet/outlet port is axial tothe housing.
 14. The fluid pressure generating means as claimed in anyone of claims 1 to 12, wherein the outflow of the fluid from theinlet/outlet port is radial to the housing.
 15. The fluid pressuregenerating means as claimed in any one of claims 1 to 12, wherein theoutflow of the fluid from the inlet/outlet port is tangential to thehousing.
 16. The fluid pressure generating means as claimed in any oneof the preceding claims, wherein a surface of the device is curved tofit snugly with the chest wall or mediastinum of a patient.
 17. Thefluid pressure generating means as claimed in any one claims 1 to 5 or 7to 16, wherein the aortic compression means is in the form of a fluidoperated cuff adapted to surround the patient's aorta.
 18. The fluidpressure generating means as claimed in any one of the preceding claims,wherein the fluid filling the housing is a liquid.
 19. The fluidpressure generating means as claimed in claim 18, wherein the liquid isan oil or saline.
 20. The fluid pressure generating means as claimed inclaim 19, wherein the oil is a silicone oil.
 21. The fluid pressuregenerating means as claimed in claim 20, wherein the oil has a viscositybetween 10 and 100 centistokes.
 22. The fluid pressure generating meansas claimed in claim 21, wherein the oil has a viscosity between 10 and30 centistokes.
 23. A heart assist device including: a blood pumpingmeans adapted, when actuated, to cause or assist the movement of bloodaround the patient's vasculature; a fluid reservoir; a fluid pressuregenerating means adapted to pump fluid from the fluid reservoir to theblood pumping means; and a housing containing both the fluid reservoirand the fluid pressure generating means that is so shaped anddimensioned as to be adapted to lie in the plueral cavity, adjacent tothe lung, when the blood pumping means is functionally positioned withinthe patient.
 24. A method for the treatment of congestive heart failure,myocardial ischemia and like conditions, the method comprising:inserting into the plueral cavity within the chest of a patient, andadjacent to the lung, a housing containing a fluid reservoir and a fluidpressure generating means adapted to pump fluid from the fluid reservoirto blood pumping means functionally placed in the patient so as to causeor assist the movement of blood around the patient's vasculature. 25.The method as claim in claim 24, wherein the housing and fluid pressuregenerating means are inserted into the plueral cavity within the rightchest of the patient.
 26. The method as claimed in claim 24 or 25,wherein the device is placed against the mediastinum directly adjacentthe patient's heart and attached to surrounding soft tissue.
 27. Themethod as claimed in any one of claims 24 to 26, wherein the device isplaced to lie in a sagittal plane within the patient's body.
 28. Themethod as claimed in any one of claims 24 to 27, wherein the device isplaced to lie without touching the inside surface of the chest wall atall.
 29. The method as claimed in any one of claims 24 to 28, whereinthe blood pumping means is adapted to displace blood in the aorta of apatient in counter-pulsation with the patient's heart.
 30. The method asclaimed in claim 29, wherein the blood pumping means is adapted todisplace blood in the ascending aorta of the patient.
 31. A heart assistdevice including: a blood pumping means adapted, when actuated, to causeor assist the movement of blood around the patient's vasculature; afluid reservoir; and a fluid pressure generating means driven by anelectric motor and adapted to pump a liquid from the fluid reservoir tothe blood pumping means; the electric motor having a cogging torquewhich is sufficiently low that the natural systolic blood pressure ofthe patient is sufficient to cause liquid in the blood pumping means tobe returned to the fluid reservoir in the event that the electric motorstops.